In a hybrid automatic repeat request (Hybrid Automatic Repeat Request, HARQ) technology, a data receiver needs to feed back acknowledgement information to a data sender to help confirm whether data is received correctly. A value of the acknowledgement information may be ACK (Acknowledgement, acknowledgment), NACK (Negative-acknowledgement, negative-acknowledgement), and DTX (Discontinuous Transmission, discontinuous transmission), where the ACK indicates that the data is received correctly, the NACK indicates that the data is received incorrectly, and the DTX indicates that no data is received.
In a 3rd Generation Partnership Project (3rd Generation Partnership Project, 3GPP) evolved universal terrestrial radio access (Evolved Universal Terrestrial Radio Access, E-UTRA) system, in an uplink (Uplink) direction, a user equipment feeds back, through a physical uplink control channel (Physical Uplink Control Channel, PUCCH), acknowledgment information corresponding to downlink data to a network side device, for example, a base station. In a downlink (Downlink) direction, the network side device feeds back, through a physical hybrid automatic repeat request indicator channel (Physical HARQ Indicator Channel, PHICH), acknowledgment information corresponding to uplink data to the user equipment. In the present invention, the PUCCH and the PHICH used to feed back acknowledgment information are called acknowledgment channels.
The 3GPP E-UTRA system is also called a Long Term Evolution (Long Term Evolution, LTE) system, and supports two standards: frequency division duplex (Frequency Division Duplex, FDD) and time division duplex (Time Division Duplex, TDD). Generally, an LTE system supporting the TDD standard is called an LTE TDD system.
In the LTE TDD system, a typical radio frame is 10 ms long, and includes 10 subframes. Each subframe is 1 ms long, and can be configured by the network side device to transmit downlink data or uplink data. The LTE TDD system supports a plurality of different subframe ratios. As shown in Table 1, D represents a downlink subframe, S represents a special subframe, and U represents an uplink subframe. The special subframe can transmit downlink data information, but cannot transmit uplink data information, and therefore is generally processed as the downlink subframe.
TABLE 1Downlink-to-uplinkSubframeswitch-pointSubframe indexratioperiodicity012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
According to the subframe ratio and an HARQ timing relationship, a plurality of downlink subframes may be associated with the same uplink subframe to feed back acknowledgement information, and a plurality of uplink subframes may also be associated with the same downlink subframe to feed back acknowledgement information. That is, according to the subframe ratio and the HARQ timing relationship, the following may be set: For downlink data transmitted in a plurality of downlink subframes, acknowledgement information of the downlink data is fed back in the same uplink frame; for uplink data transmitted in a plurality of uplink subframes, acknowledgement information of the uplink data is fed back in the same downlink subframe. The HARQ timing relationship includes a timing relationship from downlink data to corresponding uplink acknowledgement information that is fed back, and a timing relationship from uplink data to corresponding downlink acknowledgement information that is fed back.
In the LTE TDD system, when a plurality of downlink subframes is associated with the same uplink subframe to feed back acknowledgement information, acknowledgement channel resources that do not mutually overlap are reserved in the uplink subframe for each associated downlink subframe. When a plurality of uplink subframes is associated with the same downlink subframe to feed back acknowledgement information, acknowledgement channel resources that do not mutually overlap are reserved in the downlink subframe for each associated uplink subframe. The foregoing design brings about the following results: When the number of uplink subframes is smaller than the number of downlink frames in the system, the number of downlink subframes associated with the same uplink subframe is large, or when the number of downlink subframes is smaller than the number of uplink subframes in the system, the number of uplink subframes associated with the same downlink subframe is large. This means that overheads of acknowledgement channel resources reserved by the system are large. For example, for subframe ratio 2 in Table 1, acknowledgement channel resources need to be reserved in each uplink subframe for four associated downlink subframes, which causes large overheads of acknowledgment channel resources.